Reference Manual

17−7
Figure 17-11. Straight-Through Press
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.
Figure 17-12. Roll Press
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.
sheet enters the ingoing nip between the two rolls,
pressure builds and the sheet is compressed. As
pressure continues to rise, the water in the sheet
is forced out of the sheet into the press felt. This
pressure can be anywhere from 500 - 2,000
pounds per square inch where the higher the
pressure, the dryer the sheet will become.
However, press rolls normally have rubber covers
that essentially smash together. The “footprint”
that is created on the rolls, better known as the nip
width, can be larger or smaller depending on how
hard we press the rolls together. Past the
mid-point of the nip, the pressure begins to
decrease and some of the water is actually sucked
back into the sheet or re-wetted. How dry the
press can get paper is also determined by the nip
time. Generally, the roll press can increase sheet
consistency to 38 - 32% solids.
D Shoe — Rather than a roll press, some
paper machines use a shoe press (figure 17-13).
Figure 17-13. Shoe Press
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.
This type of device has a stationary roll that is
actually a hydraulically loaded stationary shoe
which is concave shaped in order to fit the other
roll. The shoe is covered by a rotating
polyurethane blanket lubricated with oil to
eliminate any type of friction between the shoe
and blanket. This creates a high pressure and long
time in the nip thus allowing for better drying
(figure 17-14). This drying can get the sheet to
approximately 50% solids.
D Fabric Press — For this type, a
multiple-weave, non-compressible fabric belt
passes through the nip between the felt and the
rubber-covered roll to provide void volume to
receive the water. The water is removed from the